Pollutants in or on the ground, or in surface or ground waters pose an increasing threat to the environment. The pollutants may result from industrial discharges, accidental spills, mine drainage, mine tailing seepage or leaks and the like. Typically, large quantities of polluted materials need to be treated so that cost of the treating materials becomes an important factor. The present invention seeks to answer this need by using low cost, readily available materials to bind the pollutants.
Heavy metals, such as mercury, arsenic, cadmium, chromium, and selenium, are used in a number of manufacturing operations and industrial and consumer products, but are hazardous to human health and the ecosystem when released to the environment. Often, heavy metals have to be removed from gas, water, or soil streams exiting a manufacturing facility or from the environment where they have already been released. The current invention proposes the use of bauxite or modified bauxite for removal of heavy metals from fluid streams (gases e.g. air or exhaust gas, liquids e.g. water), and soil or other aggregate material.
A number of different treatment processes and products have been proposed in the past for removal of these metals from the target matrices to prevent the metals from migrating to potential points of human exposure and to protect the environment. In gas streams (for example, consisting of coal-burning power plant emissions), metals are removed by using an adsorbent or catalyst. Activated carbon (Vidic R. D., Liu, W. (1997) Development of Novel Activated Carbon-Based Adsorbents for Control of Mercury Emissions From Coal-Fired Power Plants. DOE-NETL publication; Miller, S. J., Dunham, G. E., Olson, E. S., and Brown, T. D. (2000) Fuel Processing Technology 65/66:343-363; U.S. Pat. No. 6,402,813 B2) and noble metals, like molybdenum, cobalt, have been used in the past for their adsorptive and catalytic properties, respectively. A two-step process of oxidation of elemental mercury to a mercury compound, followed by its removal on an adsorbent (e.g., activated alumina) has previously been proposed (U.S. Pat. No. 5,607,496). More complex filters, for example those that involve a support material on which are synthetically deposited multiple components to address multiple pollutants, have also been proposed (U.S. Pat. No. 5,212,131).
Bauxite has sometimes been used in the past for treatment of pollutants in gases, often after expensive processing to a substance called activated bauxite. Activated bauxite is commonly generated by heating the bauxite to a temperature in the range from 400 to 1,000° C., in order to increase its surface area and improve adsorption. For example, U.S. Pat. Nos. 5,595,954 and 4,639,259 describe how activated bauxite or activated alumina (a purified form of bauxite) can be promoted by adding an alkali metal oxide to remove HCl from fluid streams. U.S. Pat. No. 4,973,459 describes the use emathlite and bauxite as sorbents for removing alkali from hot gases at temperatures up to 1,800° F., by using the sorbents in conjunction with coarse particulate materials and filter units in a moving bed. U.S. Pat. No. 4,865,629 describes a process for flitering fine particulates from a stream of hot gas by blending a fraction of particles removed by the cyclones back to the gas; this work mentions the use of diatomite or bauxite particles that can be blended into the gas stream to remove corrosive sodium and potassium vapors. U.S. Pat. No. 3,917,733 describes a two-step process for removing halogen-containing chemicals from a liquid hydrocarbon stream by using alumina or bauxite as adsorbents, and then using the spent liquid-stream adsorbents as adsorbents for treating gas streams. In all these applications, bauxite in an activated form (following heat treatment to 400° C. or above) is used primarily as an adsorbent, rather than in a raw or gently modified form as a catalyst to cause transformations of the target gas stream.
Many of these previous processes suffer from one or more of the following limitations:    1. The use of the reagent generates a waste product that interferes with its eventual reuse or disposal.    2. The reagent is too specific towards one or other target pollutant    3. A two-step process is required to obtain adequate removal of the pollutant metals. This increases the complexity of the process and cost of the treatment.    4. The reagent is relatively expensive and economic use of the reagent requires another process to regenerate and reuse the reagent.
The present invention addresses these limitations. The invention consists of a reagent that is commonly available, removes multiple pollutants, is relatively cheap and can therefore be disposed of after a single use.